DESCRIPTION: The long-term objectives of Dr. Hershfield's laboratory have been to define the pathogenic biochemical effects of inherited deficiency of the enzyme adenosine deaminase (ADA) that are responsible for causing its clinical consequences, in order to develop defective therapy. The primary consequence of ADA deficiency is Combined Immune Deficiency, which usually occurs in a "severe" form (SCID) in infants, but may also develop insidiously in older children, adolescents, or adults. The laboratory's past research on the pathogenesis of the immune deficiency has been important to the development of an effective form of enzyme replacement therapy (PEG-ADA). The laboratory is involved in monitoring treatment of patients receiving PEG-ADA, and as a result they have focused their recent research on identifying mutations responsible for causing ADA deficiency. The present proposal will continue these efforts to better define the relationship of specific mutations to the degree of enzyme deficiency metabolic and clinical severity, in response to enzyme (and gene) replacement therapy. To further this objective the investigators have proposed to systematically investigate the effects of mutations on the expression of ADA activity, using a strain of E. coli that lacks the bacterial ADA gene. They will also investigate the effects of chaperonin proteins on mutant ADA expression in order to identify mutations that cause potentially reversible effects on protein folding. It recently been learned that ADA deficient ("knockout") mice die from liver cell degeneration, and that ADA deficiency can also cause hepatitis in human patients. They will investigate the knockout mice as a model system to carry out biochemical studies that could not be done in human patients.